Medical components with microstructures for humidification and condensate management

ABSTRACT

New medical circuit components and methods for forming such components are disclosed. These components include microstructures for humidification and/or condensate management. The disclosed microstructures can be incorporated into a variety of components, including tubes (e.g., inspiratory breathing tubes and expiratory breathing tubes and other tubing between various elements of a breathing circuit, such as ventilators, humidifiers, filters, water traps, sample lines, connectors, gas analyzers, and the like), Y-connectors, catheter mounts, humidifiers, and patient interfaces (e.g., masks for covering the nose and face, nasal masks, cannulas, nasal pillows, etc.), floats, probes, and sensors in a variety of medical circuits.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Field

This disclosure relates generally to components suitable for medical useand more specifically to components that suitable for providinghumidified gases to and/or removing humidified gases from a patient,such as in positive airway pressure (PAP), respirator, anesthesia,ventilator, and insufflation systems.

Description of the Related Art

In medical circuits, various components transport naturally orartificially humidified gases to and from patients. For example, in somebreathing circuits such as PAP or assisted breathing circuits, gasesinhaled by a patient are delivered from a heater-humidifier through aninspiratory tube to a patient interface, such as a mask. As anotherexample, tubes can deliver humidified gas (commonly CO₂) into theabdominal cavity in insufflation circuits. This can help prevent “dryingout” of the patient's internal organs, and can decrease the amount oftime needed for recovery from surgery.

In these medical applications, the gases are preferably delivered in acondition having humidity near saturation level and at close to bodytemperature (usually at a temperature between 33° C. and 37° C.).Condensation or “rain-out” can form on the inside surfaces of componentsas high humidity gases cool. A need remains for components that allowfor improved humidification and condensate management in medicalcircuits. Accordingly, an object of certain components and methodsdescribed herein is to ameliorate one or more of the problems of priorart systems, or at least to provide the public with a useful choice.

SUMMARY

Medical components with microstructures for humidification and/orcondensate management and methods of manufacturing such components aredisclosed herein in various embodiments.

In at least one embodiment, a component for use in a medical circuitcomprises a first region that, in use, contacts liquid; a second regionthat is distinct from the first region; and a microstructured surface incommunication with the first region and the second region configured, inuse, to wick liquid from the first region to the second region, whereinthe microstructured surface comprises a substrate having an equilibriumcontact angle less than about π/2 radians.

In various embodiments, the foregoing component has one, some, or all ofthe following properties, as well as properties described elsewhere inthis disclosure.

The second region, in use, can be exposed to higher velocity air and thefirst region, in use, can be exposed to lower velocity air. The secondregion can be configured to communicate with a heat source. Themicrostructured surface can configured to communicate with a heatsource. The microstructured surface can comprise generally parallelmicrochannels. The microchannels can be generally square-shaped. Thecritical contact angle θ for the microchannels can satisfy the equation:

$\theta < {\arccos\left( \frac{0.5}{0.5 + X} \right)}$where X represents the height-to-width aspect ratio for the squareshaped channels. The microchannels can be generally v-shaped. Thecritical contact angle θ of the microchannels can satisfy the equation:

$\theta < {\arccos\left( {\sin\left( \frac{\beta}{2} \right)} \right)}$where β represents the angle of the v-shape. The microstructured surfacecan comprise micropillars. The micropillars can have substantially thesame cross sectional dimensions. At least some of the micropillars canhave different cross sectional dimensions from other micropillars.

In various embodiments, the foregoing component can be incorporated in amask. The mask can further comprise a drain in communication with thesecond region.

In various embodiments, the foregoing component can be incorporated in aconduit. The component can form at least a portion of an inner wall ofthe conduit. The component can be an insert in an inner lumen of theconduit. A wall of the conduit can be configured to communicate with aheat source.

In at least one embodiment, a component for use in a medical circuitcomprises a reservoir portion configured to hold a liquid; an evaporatorportion adjacent the reservoir portion configured to facilitateevaporation of the liquid; and a microstructured surface configured totransport liquid from the reservoir portion to the evaporator portion.

In various embodiments, the foregoing component has one, some, or all ofthe following properties, as well as properties described elsewhere inthis disclosure.

The evaporator portion can be heatable. The microstructured surface cancomprise microchannels having an aspect ratio that is lower near thereservoir portion and higher near the evaporator portion the aspectratio increases along a gradient. The microstructured surface cancomprise first microchannels extending generally horizontally near thereservoir portion and second microchannels extending generallyvertically near the evaporator portion, wherein the first microchannelsare configured to transport liquid to the second microchannels.

In various embodiments, the foregoing component can be incorporated in amask.

In various embodiments, the foregoing component can be incorporated in achamber suitable for use with a humidifier unit. The component can format least a portion of an inner wall of the chamber. The chamber cancomprise walls configured to be heated by a heater base of thehumidifier unit. The chamber can comprise walls configured to be heatedby a heating member distinct from the humidifier unit. The chamber canfurther comprise insulation disposed at least on or over a wall of thechamber near the evaporator portion.

In various embodiments, the foregoing component can be incorporated in aconduit. The microstructured surface can form at least a portion of aninner wall of the conduit. The microstructured surface can be disposedon an insert in an inner lumen of the conduit. A wall of the conduit isconfigured to communicate with a heat source.

In at least one embodiment, a medical circuit component for use withhumidified gas, comprises: a wall defining a space within and wherein atleast a part of the wall comprises a surface including a plurality ofmicrochannels in and on a substrate having an outward surface with anequilibrium contact angle less than about π/2 radians, the microchannelsbeing configured, in use, to wick liquid from a first region holdingliquid water to a second region exposed to an air flow to or from apatient, and the microchannels comprising first microchannels havingside portions and a bottom portion lower than the outer surface of thesubstrate and second microchannels having side portions higher than theouter surface of the substrate, wherein the side portions of the secondmicrochannels are formed by ridges around or between the firstmicrochannels.

In various embodiments, the foregoing medical circuit has one, some, orall of the following properties, as well as properties describedelsewhere in this disclosure.

The first microchannels can be generally square-shaped. The criticalcontact angle θ for the first microchannels can satisfy the equation:

$\theta < {\arccos\left( \frac{0.5}{0.5 + X} \right)}$where X represents the height-to-width aspect ratio for the squareshaped channels. The first microchannels can be generally v-shaped. Thecritical contact angle θ of the first microchannels can satisfy theequation:

$\theta < {\arccos\left( {\sin\left( \frac{\beta}{2} \right)} \right)}$where β represents the angle of the v-shape.

In some embodiments, a component for use in a medical circuit comprisesa generally horizontal, planar microstructured surface configured todisperse a liquid placed thereon. The microstructured surface can beplaced in a path of a flowing gas and a liquid dispenser can beconfigured to dispense the liquid onto the microstructured surface.

In various embodiments, the microstructured surface comprises surfaceirregularities.

In various embodiments, the surface irregularities comprise at least oneof the group consisting of granules, ridges, grooves, channels, andparticles.

In various embodiments, the liquid dispenser comprises at least onedropper configured to dispense the liquid one drop at a time on themicrostructured surface.

In various embodiments, the liquid dispenser comprises a substantiallyflat plate positioned a distance above the microstructured surface, theplate including a plurality of holes through which the liquid is able tofall onto the microstructured surface below.

These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments that implement the various features of the disclosedsystems and methods will now be described with reference to thedrawings. The drawings and the associated descriptions are provided toillustrate embodiments and not to limit the scope of the disclosure.

FIG. 1 shows a schematic illustration of a medical circuit incorporatingone or more medical tubes, a humidification chamber, and a patientinterface.

FIG. 2 shows a plan view of an example tube.

FIGS. 3A and 3B show first and second magnified longitudinal crosssections of an inner component for an example tube according to at leastone embodiment.

FIG. 4 shows a cross section of an example microstructure.

FIG. 5A shows a front perspective view of an inner component for a tube.

FIG. 5B shows a first magnified portion of the inner component of FIG.5A shown in front perspective.

FIG. 6 shows a schematic illustration of airflow velocity andtemperature profiles within a tube.

FIG. 7 shows a perspective view of an example humidification chamber.

FIG. 8A shows a perspective view of an example humidification chamber,including a first configuration of microstructures.

FIGS. 8B and 8C show front plan views of first and second magnifiedportions of the microstructures in FIG. 8A.

FIG. 8D shows a cross section of an example microstructure.

FIG. 9A shows a perspective view of an example humidification chamber,including a second configuration of microstructures.

FIGS. 9B and 9C show front plan views of first and second magnifiedportions of the microstructures in FIG. 9A.

FIG. 9D shows a cross section of an example microstructure.

FIG. 10A shows a front perspective view of an example patient interface.

FIG. 10B shows a front plan view of an example patient interfaceincorporating a conductive filament.

FIG. 11A shows a rear plan view of an example patient interfaceincluding microstructures.

FIG. 11B shows a perspective view of a magnified portion of themicrostructures in FIG. 11A.

FIG. 11C shows a cross section of an example microstructure.

FIG. 11D shows a rear plan view of an example patient interfaceincluding microstructures.

FIG. 12A shows a schematic of water droplet formation on an interfacesurface that does not incorporate microstructures.

FIG. 12B shows a schematic of water spreading on an interface surfacethat does incorporate microstructures.

FIG. 13 schematically illustrates the effect of added heat onevaporation from microstructures.

FIG. 14 is a schematic illustration of a manufacturing method of medicaltube, including a hopper feed, screw feeder to a die head, andterminating with a corrugator.

FIG. 15 is a schematic illustration of a spiral-forming manufacturingmethod for medical tubing.

FIG. 16 is a graph of example conditions for wicking in continuousmicrochannels.

FIG. 17 shows an image of a continuous microstructure.

FIGS. 18A through 18L show images of continuous and discretemicrostructures.

FIG. 19 illustrates a perspective view of a humidification chamberhaving an inlet tube incorporating microstructures.

FIG. 20 illustrates an embodiment in which a rough surface can be usedto enhance evaporation.

FIG. 21 illustrates another embodiment in which a rough surface can beused to enhance evaporation.

FIG. 22 illustrates the irregularity of the some microstructures on asurface.

FIG. 23 illustrates an embodiment of a humidification chamber thatincludes evaporations stacks or towers.

Throughout the drawings, reference numbers frequently are reused toindicate correspondence between referenced (or similar) elements. Inaddition, the first digit of each reference number indicates the figurein which the element first appears.

DETAILED DESCRIPTION

The following detailed description discloses new medical circuitcomponents and methods for forming such components, such asinsufflation, anesthesia, or breathing circuit components. As explainedabove, these components include microstructures for humidificationand/or condensate management. The disclosed microstructures can beincorporated into a variety of components, including tubes (e.g.,inspiratory breathing tubes and expiratory breathing tubes and othertubing between various elements of a breathing circuit, such asventilators, humidifiers, filters, water traps, sample lines,connectors, gas analyzers, and the like), Y-connectors, catheter mounts,humidifiers, and patient interfaces (e.g., masks for covering the noseand face, nasal masks, cannulas, nasal pillows, etc.), floats, probes,and sensors in a variety of medical circuits. Medical circuit is a broadterm and is to be given its ordinary and customary meaning to a personof ordinary skill in the art (that is, it is not to be limited to aspecial or customized meaning). Thus, a medical circuit is meant toinclude open circuits, such as certain CPAP systems, which can comprisea single inspiratory breathing tube between a ventilator/blower and apatient interface, as well as closed circuits.

Details regarding several illustrative embodiments for implementing theapparatuses and methods described herein are described below withreference to the figures. The invention is not limited to thesedescribed embodiments.

Medical Circuit

For a more detailed understanding of the disclosure, reference is firstmade to FIG. 1, which shows a medical circuit according to at least oneembodiment. More specifically, FIG. 1 shows an example breathingcircuit. Such a breathing circuit can be, for example, a continuous,variable, or bi-level positive airway pressure (PAP) system or otherform of respiratory therapy. As explained below, the breathing circuitincludes one or more medical tubes, a humidifier, and a patientinterface. Any or all of these components, and other components, of themedical circuit can incorporate microstructures for humidificationand/or condensate management. A microstructure generally may be definedas a structure having microscale dimensions in the range of 1 to 1000microns (μm) (or about 1 to 1000 μm).

Gases can be transported in the circuit of FIG. 1 as follows. Dry gasespass from a ventilator/blower 105 to a humidifier 107, which humidifiesthe dry gases. In certain embodiments, the ventilator/blower 105 can beintegrated with the humidifier 107. The humidifier 107 connects to theinlet 109 (the end for receiving humidified gases) of the inspiratorytube 103 via a port 111, thereby supplying humidified gases to theinspiratory tube 103. An inspiratory tube is a tube that is configuredto deliver breathing gases to a patient. The gases flow through theinspiratory tube 103 to the outlet 113 (the end for expelling humidifiedgases), and then to the patient 101 through a patient interface 115connected to the outlet 113. In this example, outlet 113 is a Y-pieceadapter. An expiratory tube 117 also connects to the patient interface115. An expiratory tube is a tube that is configured to move exhaledhumidified gases away from a patient. Here, the expiratory tube 117returns exhaled humidified gases from the patient interface 115 to theventilator/blower 105. The inspiratory tube 103 and/or expiratory tube117 according to at least one configuration can comprisemicrostructures. These tubes (and others) are described in greaterdetail below.

In this example, dry gases enter the ventilator/blower 105 through avent 119. A fan 121 can improve gas flow into the ventilator/blower bydrawing air or other gases through vent 119. The fan 121 can be, forinstance, a variable speed fan, where an electronic controller 123controls the fan speed. In particular, the function of the electroniccontroller 123 can be controlled by an electronic master controller 125in response to inputs from the master controller 125 and a user-setpredetermined required value (preset value) of pressure or fan speed viaa dial 127.

The humidifier 107 comprises a humidification chamber 129 containing avolume of water 130 or other suitable humidifying liquid. Preferably,the humidification chamber 129 is removable from the humidifier 107after use. Removability allows the humidification chamber 129 to be morereadily sterilized or disposed. However, the humidification chamber 129portion of the humidifier 107 can be a unitary construction. The body ofthe humidification chamber 129 can be formed from a non-conductive glassor plastics material. But the humidification chamber 129 can alsoinclude conductive components. For instance, the humidification chamber129 can include a highly heat-conductive base (for example, an aluminumbase) contacting or associated with a heater plate 131 on the humidifier107. By way of example, the humidifier 107 may be a standalonehumidifier, such as any of the humidifiers in the respiratoryhumidification range of Fisher & Paykel Healthcare Limited of Auckland,New Zealand. An example humidification chamber 129 is described in U.S.Pat. No. 5,445,143 to Sims, which is incorporated by reference in itsentirety.

A humidification chamber 129 according to at least one embodiment cancomprise microstructures and is described in further detail herein.

The humidifier 107 can also include electronic controls. In thisexample, the humidifier 107 includes an electronic, analog or digitalmaster controller 125. Preferably, the master controller 125 is amicroprocessor-based controller executing computer software commandsstored in associated memory. In response to the user-set humidity ortemperature value input via a user interface 133, for example, and otherinputs, the master controller 125 determines when (or to what level) toenergize heater plate 131 to heat the water 130 within humidificationchamber 129.

Any suitable patient interface 115 can be incorporated. Patientinterface is a broad term and is to be given its ordinary and customarymeaning to a person of ordinary skill in the art (that is, it is not tobe limited to a special or customized meaning) and includes, withoutlimitation, masks (such as tracheal mask, face masks and nasal masks),cannulas, and nasal pillows. A temperature probe 135 can connect to theinspiratory tube 103 near the patient interface 115, or to the patientinterface 115. The temperature probe 135 monitors the temperature nearor at the patient interface 115. A heating filament (not shown)associated with the temperature probe can be used to adjust thetemperature of the patient interface 115 and/or inspiratory tube 103 toraise the temperature of the inspiratory tube 103 and/or patientinterface 115 above the saturation temperature, thereby reducing theopportunity for unwanted condensation.

The patient interface 115 according to at least one embodiment cancomprise microstructures and is described in greater detail below.

In FIG. 1, exhaled humidified gases are returned from the patientinterface 115 to the ventilator/blower 105 via the expiratory tube 117.The expiratory tube 117 can have a temperature probe and/or heatingfilament, as described above with respect to the inspiratory tube 103,integrated with it to reduce the opportunity for condensation.Furthermore, the expiratory tube 117 need not return exhaled gases tothe ventilator/blower 105. Alternatively, exhaled humidified gases canbe passed directly to ambient surroundings or to other ancillaryequipment, such as an air scrubber/filter (not shown). In certainembodiments, the expiratory tube is omitted altogether.

As discussed above, the inspiratory tube 103, expiratory tube 117,humidification chamber 129, and/or patient interface 115 of the examplemedical circuit can comprise microstructures. A discussion of thesecomponents follows. The invention is not limited by these embodiments,however, and it is contemplated that the disclosed microstructures canbe integrated into a variety of medical components that contact and/ortransport humidified gases, such as humidified air.

Medical Tube with Microstructures

FIG. 2 shows a perspective view of a tube 201 suitable for use in amedical circuit, according to at least one embodiment. As shown in FIG.2, the tube 201 can be corrugated, which advantageously improves thetube's flexibility. However, the tube 201 can have a relatively smooth,non-corrugated wall in certain embodiments.

In certain embodiments, the tube 201 can be used for transporting gasesto and/or from infant or neonatal patients. In certain embodiments, thetube 201 can be used for transporting gases to and/or from standardpatients, such as older children and adults. Some example dimensions of“infant” and “standard” medical tubes described herein, as well as somepreferred ranges for these dimensions, are described in commonly ownedU.S. Provisional Patent Application Nos. 61/492,970, filed Jun. 3, 2011,and 61/610,109, filed Mar. 13, 2012, and in commonly owned InternationalPublication No. WO 2011/077250 A1, each of which is incorporated byreference in its entirety. An example length for infant and standardtubes can be 1 to 2 m (or about 1 to 2 m).

In at least one embodiment, the tube 201 is formed from an extrudatecomprising one or more polymers. Preferably the polymer is selected sothat the resulting tube 201 is generally flexible. Preferred polymersinclude Linear Low Density Polyethylene (LLDPE), Low DensityPolyethylene (LDPE), Polypropylene (PP), Polyolefin Plastomer (POP),Ethylene Vinyl Acetate (EVA), Plasticized Polyvinylchloride (PVC), or ablend of two or more of these materials. The polymer(s) forms at least98.4 (or about 98.4), 98.5 (or about 98.5), 98.6 (or about 98.6), 98.7(or about 98.7), 98.8 (or about 98.8), 98.9 (or about 98.9), 99.0 (orabout 99.0), 99.1 (or about 99.1), 99.2 (or about 99.2), 99.3 (or about99.), 99.4 (or about 99.4), 99.5 (or about 99.5), 99.6 (or about 99.6),99.7 (or about 99.7), 99.8 (or about 99.8), or 99.9 (or about 99.9)weight percent (wt. %) of the total extrudate. In particularembodiments, the extrudate comprises 99.488 (or about 99.488) wt. % orabout 99.49 (or about 99.49) wt. % LLDPE. In certain embodiments, thetube 201 is formed from a foamed polymer as described in commonlyassigned International Publication No. WO 2001/077250 A1, which isincorporated by reference in its entirety.

In some embodiments, microstructures may be formed of soft metalmaterials, such as aluminum foil, brass, and copper. In some suchembodiments, the materials selected can have a high surface energy. Insome embodiments, the substrate materials can be coated and can includean additive that increases the surface energy of the substrate material.In some embodiments, the use of the metal alone without being formedinto microstructures may be advantageous simply because of the highsurface energy. But microstructures may be formed of the metals, forexample, by first forming the soft metal into a film or a thin film andsubsequently stamping the material to form microstructures. The stampedmaterial may then be used to form any number of suitable components inthe humidification devices of the present disclosure. For example, atleast an interior portion of the tube 201 may formed of a metal that mayor may not have been stamped to form microstructures. And in someembodiments, a stamped metallic film may form a surface on any number ofstructures (walls, towers, fins, base, etc.) within a humidificationchamber.

In certain embodiments, a tube 201 can comprise one or more conductivefilaments. In certain embodiments, the tube 201 can comprise two or fourconductive filaments, and pairs of the conductive filaments can beformed into a connecting loop at one or both ends of the tube 201. Theone or more filaments can be disposed on the outside of the tube 201,for example, spirally wound around the outside of the tube 201, ordisposed on the inner wall of the tube 201, for example, spirally woundaround along the lumen wall. Filaments are discussed in greater detailbelow.

It was discovered that interaction between liquids and surfacesincluding purpose-built microstructures can result in spreading of theliquid onto the surface and inside or on the microstructures. Thisinteraction was further discovered to increase the liquid-vaporinterface area and reduce the thickness of the liquid layer on top ofthe surface. The combination of increased surface area and reducedthickness improve liquid evaporation, compared to liquid of the samevolume of liquid on a flat surface. As discussed below, the combinationof increased surface area, reduced thickness, and heating furtherimproves liquid evaporation. Accordingly, in various embodiments, theinner walls of the tube 201 comprise microstructures 301, as shown inFIG. 3A (not to scale). A first magnified view of a portion of themicrostructures 301 is shown in FIG. 3B. FIG. 3B shows themicrostructures 301 at a greater magnification than FIG. 3A. In FIGS. 3Aand 3B, the microstructures 301 are axially disposed along the tube 201(that is, the microstructures extend in a direction perpendicular tolongitudinal length of the tube 201).

Polymers generally have a low surface energy, resulting in poorwettability. In order to improve the water spreading capabilities of themicrostructures 301 on a polymer tube 201, it can be advantageous totreat the one or more polymers with a material or materials forincreasing the surface energy. Surfactants, such as cationicsurfactants, can be particularly desirable additive materials. Suitablesurface modifying agents include glycerol monostearate (GMS),ethoxylated amine, alkanesulphonate sodium salt, and lauricdiethanolamide and additives comprising these substances. MLDNA-418supplied by Clariant (New Zealand) Ltd. and under the product name “418LD Masterbatch Antistatic” is a surface modification agent master batchwith 5 (±0.25)% glycerol monostearate (CAS No. 123-94-4) as an activeingredient. Preferably the surface modifying agent comprises at leastabout 0.05 (or about 0.05), 0.1 (or about 0.1), 0.15 (or about 0.15),0.2 (or about 0.2), 0.25 (or about 0.25), 0.3 (or about 0.3), 0.35 (orabout 0.35), 0.4 (or about 0.4), 0.45 (or about 0.45), 0.5 (or about0.5), 1.1 (or about 1.1), 1.2 (or about 1.2), 1.3 (or about 1.3), 1.4(or about 1.4), or 1.5 (or about 1.5) wt. % of the total extrudate. Forexample, in at least one embodiment, the tube extrudate comprises 0.25wt. % (or about 0.25 wt. %) of surface modifying agent. As anotherexample, in at least one embodiment, the tube extrudate comprises 0.5wt. % (or about 0.5 wt. %) of surface modifying agent.

Other materials, such as other surfactants or other hydrophilizingagents, could also be utilized to improve the water spreadingcapabilities of the tubes 201 or other embodiments. For example, anysuitable anionic, cationic or non-ionic surfactants or otherhydrophilizing agents, or combinations of such surfactants orhydrophilizing agents can be used. Suitable hydrophilizing agents can beany agent or agents generally capable of increasing the hydrophiliccharacter of a composition. In some configurations, the surfactant orhydrophilizing agent can comprise an ethoxylized fatty alcohol, such asthose described in EP 0 480 238 B1, the entirety of which isincorporated by reference herein. In some configurations, the surfactantor hydrophilizing agent can comprise a non-ionic surface-activesubstance, such as the nonylphenolethoxylates, polyethyleneglycol-monoesters and diesters, sorbitan esters, polyethyleneglycol-monoethers and diethers and others described in EP 0 268 347 B1,or a non-ionic perfluoralkylated surface-active substance, such as thosedescribed in WO 87/03001, the entireties of which are incorporated byreference herein. In some configurations, the surfactant orhydrophilizing agent can contain silicon moieties. In someconfigurations, the surfactant or hydrophilizing agent can comprise awetting agent, such as hydrophilic silicon oils as described in theabove-mentioned WO 87/03001 and EP 0 231 420 B1, the entirety of whichis incorporated by reference herein. In some configurations, thesurfactant or hydrophilizing agent can comprise polyether carbosilanes,such as those described in WO 2007/001869, particularly at pages 13 and14, the entirety of which is incorporated by reference herein. Othersuch suitable agents are described in U.S. Pat. No. 5,750,589, U.S. Pat.No. 4,657,959 and EP 0 231 420 B1, as referenced in WO 2007/001869, theentireties of which are incorporated by reference herein. In someconfigurations, the surfactant or hydrophilizing agent can compriseethoxylated surfactants containing a siloxane solubilizing group, suchas those described in the above-mentioned U.S. Pat. No. 4,657,949 andWO2007/001869. Examples of such ethoxylated surfactants are the SILWET®line of surface active copolymers (e.g., SILWET® L-77) available fromMomentive Performance Materials, Inc. of Albany, N.Y. USA and the MASIL®SF19 available from Emerald Performance Materials, LLC of CuyahogaFalls, Ohio USA.

Other methods can also be used to increase surface energy. Suitablemethods include physical, chemical, and radiation methods. Physicalmethods include, for example, physical adsorption and Langmuir-Blodgettfilms. Chemical methods include oxidation by strong acids, ozonetreatment, chemisorption, and flame treatment. Radiation methods includeplasma (glow discharge), corona discharge, photo-activation (UV), laser,ion beam, electron beam, and gamma irradiation.

By selecting a suitable surface modification method or agent, it ispossible to provide a tube wall having surface property contact anglesof less than 50 (or about 50), 45 (or about 45), 40 (or about 40), 35(or about 35), 30 (or about 30), 25 (or about 25), 20 (or about 20)degrees (°), as measurable by an angle measurement device such as agoniometer. For instance, tube walls having surface property contactangles of less than 35° (or about 35°) provide useful results.Desirably, the contact angle is less than π/2 (or about π/2). Moredesirably, the contact angle is 0° or about 0°.

TABLE 1 below shows contact angle measurements for various LLDPEsamples, including a sample treated with a surface-modifying agent and asample treated with radiation. The contact angle measurements were basedon static drop shape testing methods conducted in accordance with ASTMStandard D7334, 2008, “Standard Practice for Surface Wettability ofCoatings, Substrates and Pigments by Advancing Contact AngleMeasurement.”

TABLE 1 Average Contact Description of Surface Liquid Angle (degrees)Linear Low-density Polyethylene Water 97.39 (LLDPE), as manufacturedLinear Low-density Polyethylene Water 67.56 (LLDPE), fluorinated, washedLinear Low-density Polyethylene Water 44.98 (LLDPE), plasma-treated, 10%O₂, 300 Watts, 30 seconds Linear Low-density Polyethylene Water 33.09(LLDPE), with 5% MLDNA-418 as surface modification agent additive

The sample with 5% MLDNA-418 surface modifying agent produced the lowestmeasured contact angle compared to other surface modification methodstested.

As discussed above, in certain embodiments, the additive material isadded to the bulk polymer extrudate. It can be desirable to add thematerial in the polymer matrix so that the additive material replenishesthe surface for the useful life of the tube. In certain configurations,the material can be added as a surface treatment on the polymer, forexample, by coating a surface of the polymer with the material. Forexample, a microstructured surface can be brushed, sprayed, or otherwisecoated with additive material such as HYDRON anti-fog coating (MXLIndustries, Lancaster, Pa.), EXXENE anti-form coatings such as HCAF-100(Exxene Corporation, Corpus Christi, Tex.), and MAKROLON anti-fog (BayerCorporation) to produce a thin (e.g., 1 μm or thereabout) coating ofadditive material. A surface coating can be desirable because of lowcosts and ease of manufacture.

In certain configurations, a thin film of hydrophilic material such asbreathable polyurethanes, for example, ESTANE 58245 (LubrizolCorporation, Wickliffe, Ohio), breathable polyesters, for example,ARNITEL VT3108 (DSM Engineering Plastics, Sittard, Netherlands), orbreathable polyamides, for example PEBAX (Arkema, Colombes, France) canbe cast as a surface modifying agent. These hydrophilic materials canabsorb moisture and become very wettable. An example method ofimplementing the hydrophilic thin film includes dissolving thebreathable polymer in a solvent, casting the mixture, and allowing thesolvent to evaporate, thus leaving a thin film of the breathablematerial on the microstructures. For instance, ESTANE 58245 pellets canbe dissolved in a tetrahydrofuran (THF) of dimethylformamide (DMF)solvent and cast onto microstructures machined from brass or aluminumusing a micromilling process. Typical dimensions for the thin film arein the range of 1 to 10 μm (or about 1 to 10 μm). Preferably, thesolvent, breathable material, and microstructure material combination isselected such that the microstructure shape and quality is notsubstantially influenced, for example, by dissolving the microstructureswith the solvent.

Certain embodiments include the realization that the perpendicularconfiguration shown in FIGS. 3A and 3B can advantageously improvehumidification and condensate management. As shown in FIG. 1, a tube(e.g., 103 and 117) generally extends in a horizontal direction,although certain portions can extend vertically, particularly near theends of the tube, and some portions can be sloped. Under the action ofgravity, condensate tends to run down the vertical and sloped portionsof the tube and pool at the lowest points of the generally horizontaltube. When microstructures are perpendicular to the generally horizontaltube bottom, the microstructures will move pooled condensate vertically,against gravity. This action increases the amount of condensate on thetube walls and, thus, the surface area of condensate exposed to the airstream. Exposing a greater surface area of condensate to the air streamincreases the likelihood that the condensate will evaporate into the airstream. Therefore, the perpendicular configuration reduces thecondensate pooled in the tube and improves the likelihood that the airflowing through the tube maintains a desired level of humidity nearsaturation.

This configuration can be advantageous because it causes minimaldisruption to the airflow within the tube lumen, as there are nostructures extending into the lumen. At least one embodiment includesthe realization that microstructures do not have to extend into or coverthe lumen in order to enhance evaporation.

According to some embodiments, microstructures may be oriented in thedirection of the tube. For example, FIG. 19 illustrates an embodiment ofchamber 129 to which is attached at the inlet 701 a tube 1901incorporating microstructures 1903. The tube 1901 may be located at theinlet 701 of the evaporation chamber 129. A liquid, such as water, canbe dispensed into the tube 1901 some distance above the inlet 701 sothat the water runs through and along the microstructures 1903 in thedirection of the humidification chamber 129.

In some configurations, the liquid can be metered onto the inner surfaceof the tube 1901 such that a controlled introduction spreads the liquidaround the circumference and, through the use of the microstructures andgravity, along the inner surface of the tube 1901. The introduction ofliquid can be controlled using any suitable rate limiting device. Therate of water flowing into the tube 1901 may be regulated using the ratelimiting device to maximize the interplay between the water themicrostructures 1903 in the tube 1901. For example, increasing theamount of water in the tube 1901 may increase the amount of evaporationthat occurs. However, the microstructures 1903 may be most effective ifnot completely covered or coated in water. It has been found thatevaporation occurs on a rough surface primarily along the edges of thewater and the surrounding structure. Accordingly, it may be desirable tocontrol the amount of water flowing through the tube 1901 so as tomaximize the number of edges against the water.

In some configurations, a liquid supply tube can extend between the ratelimiting device and a collar. The collar can include microchannels on anouter surface of a sleeve, which microchannels can be in communicationwith the microchannels on the tube 1901. As such, the collar can be usedto supply liquid to the tube 1901. Moreover, the collar can include anouter surface to which the gas supply conduit can connect. Air flowingdown or through the tube 1901 toward the humidification chamber 129begins to evaporate and carry away the water from the inner surface ofthe tube 1901. Thus, the air reaching the humidification chamber 129 hasalready acquired at least some water vapor.

In some embodiments (not shown), a heat jacket may also be incorporatedinto, or may surround, at least a portion of the tube 1901. The heatjacket can further enhance the evaporation of the water or liquid intothe flowing gas. In some embodiments, rather than having a heat jacketor in addition to having a heat jacket, the tube 1901 can have heatersprinted onto one or more portion of the tube 1901. In some embodiments,the tube 1901 can include structures such as thick film heatingelements, etched foil or wire elements to provide a heating element.

The tube 1901 with the microstructures 1903 may be formed in anysuitable manner and using any suitable materials. In some embodiments,the tube 1901 can be formed of a corrugated sheet formed from ahydrophilic polymer. Once formed, the corrugated material can be wrappedto form the tube 1901 with the microstructures 1903 running at least aportion of the length of the inner surface of the resulting structure.In some embodiments, the microstructures 1903 are V-shaped trenches. Insome embodiments, the V-shaped trenches comprise troughs that are about30 μm apart from neighboring troughs when the sheet is laid out flat. Insome configurations, the sheet, and therefore the resulting tube 1901,may be about 150 mm long and, once folded to form tube 1901, may have adiameter of about 20 mm.

FIG. 4 illustrates a cross section of an example microstructure 301. Inthis example embodiment, the microstructure 301 is a continuousmicrochannel with a wedge-like structure. A continuous microchannelgenerally may be defined as a continuous channel having dimensions of1000 μm (or about 1000 μm) or smaller. In at least one embodiment, themicrochannel has a depth d of 20-40 μm (or about 20-40 μm), a maximumwidth w of 20 μm (or about 20 μm), and an angle θ of 30-60° (or about30-60°). In certain embodiments, a tube surface has amicrochannel-to-solid ratio of 1:1 (or about 1:1). The foregoingdimensions are not limiting, and additional suitable dimensions arediscussed in greater detail below. Because of the scale differencesbetween these example embodiments and the example tube dimensionsdiscussed above, microstructured surfaces can reside and operate in anopen system, rather than a closed system, such as a lab-on-a-chip.

Certain embodiments include the realization that movement of liquid in amicrochannel is primarily based on surface forces, rather than inertialforces or gravitational forces. Certain embodiments also include therealization that surface forces generally dominate if the characteristicdimension of the microstructure is smaller than the capillary length(L_(c)), defined as

${L_{c} = \sqrt{\frac{\gamma}{\rho\; g}}},$where γ represents surface tension, ρ represents the fluid density, andg represents the gravitational acceleration constant (9.8 m/s²). Forwater at room temperature, capillary length is about 2.3 mm. Inaccordance with the foregoing realizations, microscale dimensions lessthan about 2.3 mm can result in observable surface phenomena for waterat room temperature. It was discovered, however, that the size ofmicrostructures does not always dictate whether there is observablecapillary wicking, an increase in surface area, and/or or reduction infilm thickness. Accordingly, in certain embodiments, the microstructuresincludes a base substrate having an equilibrium contact angle less thanπ/2 (or about π/2). Under isothermal (or nearly isothermal) conditionsand on a length scale smaller than capillary length, a criterion forwicking can be defined that depends on the aspect ratio of themicrostructure and a critical equilibrium contact angle. For a squaretrench, the relation can be expressed as

$\theta_{crit} = {\arccos\left( \frac{0.5}{0.5 + X} \right)}$where X is the height to width aspect ratio. For a v-shaped groove, therelation can be expressed as

$\theta_{crit} = {\arccos\left( {\sin\left( \frac{\beta}{2} \right)} \right)}$where β is the angle of the groove's wedge. FIG. 16 is a graph ofexample conditions for wicking in continuous microchannels, specificallysquare (1601) and v-shaped (1603) grooves. In the area below the curves,wicking into the channels tends to occur. In the area slightly above thecurves, droplet stretching into a number of meta-stable equilibria isobserved, but wicking tends not occur. In the area well above thecurves, droplet stretching is not observed and wicking does not occur.Different combinations of surface wettability and channel aspect ratiowill result in liquid wicking into the microchannels, provided that thecharacteristic dimension is smaller than the capillary length for theliquid (so that surface tension forces dominate over viscous forces). Ingeneral, however, liquid will wick into the channels if conditions aresuch that θ_(crit) is below the curves.

In accordance with the above realizations, it was determined that, topromote wicking, structures with high aspect ratios and/or high surfaceenergy (low contact angles) are desirable. Surfactants, such as thosediscussed above, can result in contact angles near 0°, so wicking cantake place with ease. The equilibrium contact angle over most polymersurfaces is greater than about 0.87 rad (about 50°), so deeper channelscan be implemented to facilitate wetting.

Surface roughness or microstructures (e.g., regular microstructures) canpromote the dispersion of liquid droplets and, therefore, can reduce thethickness/depth of the droplets, which increases the liquid/vaporsurface area when the equilibrium contact angle is less than about 90°.The surface roughness of microchannels also can play a role in wicking.It is believed that microstructured or nanostructured bumps within themicrochannels could act to pin the solid/liquid/vapor contact line,increase surface area, and/or act as nucleating sites for condensation.FIG. 17 shows microchannels similar to those shown in FIG. 18C, butviewed using an environmental scanning electron microscope. Roughnesscan clearly be seen on the surface. In some configurations, surfaceroughness can have a detrimental effect on spreading and evaporation ifthe contact angle is greater than about 90° because the liquid dropletswill spread less, which will reduce the liquid/vapor surface area. Forat least this reason, constructions having an equilibrium contact angleof less than about 90° are generally preferred.

Many different shapes of microstructures can achieve desirable results.For example, the continuous microchannel profile can be sinusoidal or asharp trench. In certain embodiments, the microchannel has an aspectratio that increases with distance, for example, a chemical or physicalgradient. In some embodiments, a channel depth gradient is used tocontrol movement of a liquid in a particular direction. It has beenfound that liquids tend to move in the direction of the deeper channels.A gradient can be desirable because, provided that hysteresis is slow,the substrate can force a droplet to move toward an area of higherenergy in order to lower it. Gradients can also speed up or otherwiseimprove the wicking of liquid. For example, in some embodiments, achannel depth gradient is used to move liquid toward a region of higherair flow thereby increasing evaporation. In some embodiments, largerchannels are used along vertical walls of a structure to direct waterfrom the bottom of the structure to the top of the corrugated structurethereby bringing the water closer to a heating element for evaporation.

Furthermore, the microstructure need not be continuous. Discretemicrostructures help liquid to disperse thereby acceleratingevaporation. It has been found that on a rough surface, most evaporationhappens around the transition of the solid structure and the liquid(i.e., at the edges of the liquid). Accordingly, increasing theroughness of the overall structure increases the transition areas andimproves evaporation. For example, a surface can comprise discretefeatures such as cylindrical, pyramidal, or cube-shaped posts orpillars. Microstructures can also comprise a hierarchy of the foregoingfeatures. In some embodiments, discrete features are uniform orpartially uniform. In some embodiments, the discrete features arerandomly distributed on a surface. For example, some embodiments utilizecrystals having irregular shapes spread across or adhered to a surface.In some embodiments, an irregular surface (i.e., not smooth) canadvantageously improve evaporation.

FIGS. 20 and 21 illustrate embodiments that utilize irregular or roughsurfaces to enhance evaporation of a liquid. FIG. 20 illustrates that aliquid may be applied to a rough surface 2001 using a dispensingmechanism 2003 located some distance D from the surface 2001 thatoutputs small amounts of the liquid. In some configurations, the dropsare emitted as one drop at a time. In some configurations, the drops cansplash upon contact, which results in smaller droplets.

Each drop may contact the rough or irregular surface 2001 and quicklyspread across the surface 2001 thereby enhancing the evaporation of theliquid into a gas that flows over the surface 2001. In some embodiments,the surface 2001 is heated to further enhance the evaporation of theliquid into the passing gas. While the embodiment in FIG. 20 has beenshown with only a single liquid dispenser 2003, or dropper, someembodiments, as shown in FIG. 21, may comprise more than one liquiddispenser 2003. Multiple liquid dispensers 2101 can be located atvarious locations over the surface 2001 to increase the coverage of theliquid on the surface 2001. In some embodiments (not shown), a surfacecomprising a plurality of holes serves as the liquid dispenser 2101. Aliquid, such as water, is allowed to flow over the surface. The liquidthen drips or falls through the plurality of holes in the surface downto the rough or irregular surface 2001 below. A gas may flow between thetwo surfaces (i.e., the first surface and the rough or irregular surface2001) and evaporates the liquid as it falls and after is disperses amongthe microstructures of the rough or irregular surface 2101. FIG. 21further illustrates that in some embodiments, the flow of a gas, such asair that is to be humidified, can be channeled or shaped to form arelatively flat stream over the rough surface 2001. Such a configurationmay force more of the gas to interact with the rough surface 2001.

FIG. 22 illustrates one type of rough surface that includes a pluralityof ridges 2201 having varying heights and widths. It is believed thatrough surfaces having higher height to width ratios (e.g., steeperslopes) spread liquids and increase evaporation. In some configurations,having steeper slopes is believed to increase the number of contactlines. In some embodiments, increasing the number of contact linesbetween the liquid and the rough surface is believed to increaseevaporation. In some embodiments, the presence of taller ridges 2201 mayincrease the number of contact lines between the liquid and the roughsurface thereby increasing evaporation relative to a surface havingshorter ridges 2203. In some embodiments, the use of heat applied torough surface may increase the rate of evaporation particularly at thecontact lines. In some embodiments, the use of a surface having integralmicrostructures, namely microstructures integrally connected to theunderlying surface, may allow for better heat transfer if the underlyingsurface is heated. Such a configuration may improve the ability of heatto assist in the evaporation of the liquid.

Although the discussion above regarding FIGS. 20-22 refers to rough orirregular surfaces, a microstructured surface having a regular patternmay achieve similar results. Similar to droplets on a rough surface,droplets on a surface with microstructures will disperse and evaporateinto a passing gas more quickly than a smooth surface having nomicrostructures or surface irregularities. In some embodiments, themicrostructures are uniform. In some embodiments, the microstructuresare sized and arranged according to a pattern if not everymicrostructure is the same.

If the wicking criteria discussed above are satisfied, then water willwick into the microchannels and/or micropillars with certain dynamics,termed Lucas-Washburn dynamics. The wicking length (L) increasesproportional to the square root of time (t) (L=A√{square root over(t)}), regardless of the shape of the channel or the aspect ratio, solong as it is of a uniform cross section. A is a function of surfacetension, viscosity, the cross sectional area of the channel, and thecontact angle. Thus, what determines the strength of this relationship(i.e., the value of A) depends on some or all of these parameters.

Certain embodiments include the realization that low contact angles,high aspect ratios, high surface tension, and low viscosity can lead toimproved wicking. Because wicking length is proportional to the squareroot of time, the velocity of wicking is inversely proportional tolength and inversely proportional to the square root of time. Statedanother way, wicking slows down with distance and with the passage oftime.

FIGS. 18A through 18L show images of continuous and discretemicrostructures. The substrate material in FIG. 18A is polyethyleneterephthalate (PET). The substrate material in the other figures is anacrylic. The v-shaped grooves in FIG. 18A were cut using a double-edgerazor blade. The other microstructures were fabricated using a 3Dprinter (ProJet HD 3000). In some embodiments, microstructures orsurfaces incorporating microstructures can be manufactured by directinjection molding or hot embossing. Although not shown in these figures,it is also possible to machine microstructures using a CNC machineequipped with micro-end mills, such as those sold by Performance MicroTool (Janesville, Wis.). FIGS. 18B and 18C show square-shaped grooves.FIG. 18D shows a front view of a square microchannel array having agradient in topography, and specifically shows the front view of thelong end of the microchannels. FIG. 18E shows a front view of the shortend of the microchannels of FIG. 18D. FIG. 18F shows a side view of asquare microchannel array of FIG. 18D. As discussed herein, with agradient in the topography, the dynamics of wicking (specifically, thespeed-time relation) can potentially be modified by havingmicrostructures that change in depth with distance. This topography candesirably influence the way that liquid evaporates and condenses on thesurface. Such variable depth configurations can be achieved byembossing, machining, or casting. FIG. 18G shows a droplet on squaregrooves that have not been treated with a surfactant. FIG. 18H showsspreading of a droplet on square grooves that have been treated with asurfactant. FIGS. 18I and 18J show top-down views of a pillared surfaceat different magnifications. FIG. 18K shows a side view of the pillaredsurface. FIG. 18L shows another embodiment of a microstructure defininga surface shape that is an inverse of the shape of the microstructure ofFIG. 18A. The microstructure of FIG. 18L comprises alternating tallerridges and shorter ridges, each of which are separated from one anotherby a small channel or first microchannel. Preferably, the taller ridgesare substantially taller than the shorter ridges and may be 2-3 times astall, or taller, than the shorter ridges. In the illustratedarrangement, the shorter ridges are substantially wider than the tallerridges, such as about 3-5 times wider, for example. The small channelscan be any suitable size, such as about the width of the taller ridges,for example. In addition, the taller ridges define large channels orsecond microchannels therebetween, which can communicate with or becontiguous with the small channels. A depth of the large channels can belarger than a depth of the small channels, such as up to 2-3 times aslarge, or larger. The small channels can be generally triangular incross-sectional shape, while the large channels can have across-sectional shape generally similar to an inverted trapezoid.Because the shorter ridges preferably define a significantly larger areathan the taller ridges, the upper surfaces of the shorter ridges can beviewed as the outer surface of the material or substrate, with the smallchannels being recessed from the outer surface and the taller ridgesprojecting from the outer surface.

The microstructures 301 can extend along the entire length of the tube201 or along a portion of the length of the tube 201, such as a centralportion that is likely to collect condensate. Alternatively, themicrostructures 301 can extend along the tube 201 at regular orirregular intervals, separated by portions with no microstructures. Theforegoing figures show the microstructures 301 encircling the innercircumference of the tube 201. The microstructures 301 need not encirclethe entire inner circumference in all embodiments, however. For example,microstructures 301 can be disposed around half or quarter of thecircumference.

It was discovered that a single drop of liquid can spread many times itsdiameter and a very efficient evaporation of liquid can be achieved ifheat is supplied to the substrate beneath the liquid. Accordingly, incertain embodiments, the one or more filaments discussed above compriseheating filaments. Heating filaments can be embedded or encapsulated inthe wall of the tube 201. For example, the one or more filaments can bespirally wound in the wall of the tube 201 around the tube lumen. Theone or more filaments can be disposed within the tube 201, for example,in a spirally-wound configuration as described in U.S. Pat. No.6,078,730 to Huddard et al., which is incorporated in its entirety bythis reference. The arrangement of heating filaments is not limited toone of the foregoing configurations. Furthermore, heating filaments canbe arranged in a combination of the foregoing configurations.

In certain embodiments, the tube 201 comprises an inner componentcomprising microstructures. An example inner component 501 is shown inFIG. 5. An magnified view of the inner component 501 is shown in FIG.5B. The example inner component 501 is a serrated strip. The serrationsin the inner component 510 can be sized and configured to complement thecorrugations of the tube (not shown), such that the tube generally holdsthe inner component 501 in place. In FIG. 5B, microstructures 301 extendvertically to cover both axial surfaces of the inner component 501 alongthe longitudinal length of the inner component 501. Alternatively,microstructures 301 can cover one axial surface. In certainconfigurations, microstructures 301 can extend along a portion of thelongitudinal length or along regular or irregular intervals of thelongitudinal length. An inner component 501 can comprise more than oneserrated strips. For example, an inner component can comprise twoserrated strips and resembles a plus-sign having serrations along thelongitudinal length. These embodiments are not limiting. A larger numberof strips can be incorporated. However, it can be advantageous to have alower number of strips to improve the airflow through the tube lumenand/or improve tube flexibility.

Inclusion of an inner component 501 can be advantageous because theinner component 501 can allow microstructures 301 to extend into thetube lumen and reach the center of the tube 201 lumen. As shown in FIG.6, airflow velocity increases from the tube wall to the center of thetube lumen (centerline) and reaches a maximum at the centerline. Thus,water rising up the microstructures 301 in FIGS. 5A and 5B is exposed tothe warm, higher velocity air flow. Exposing the condensate to thehigher air velocity near the center of the tube increases the likelihoodthat the condensate will evaporate into the air stream.

Alternative configurations are possible for the inner component 501. Forexample, the inner component 501 can be wound inside a tube 201. Thisconfiguration can be desirable because it allows the microstructures toextend a distance into the tube 201 lumen, which is exposed to higherairflow velocity than the tube 201 walls. In at least one embodiment,the inner component 501 is wound so that at least a portion of the innercomponent 501 crosses the center of the tube lumen.

As noted above, it was discovered that the addition of heat to amicrostructured surface can dramatically improve evaporation rates.Accordingly, the inner components 501 of any of the foregoingembodiments can incorporate a heating filament, which can improveheating of the airflow along the tube and, thus, the likelihood thatcondensate in the microchannels will evaporate into the airflow.Incorporating one or more heating filaments into the inner component 501also decreases the likelihood that condensation will occur on the warminner component. It was discovered that evaporation is highest at thecontact region, where the solid surface, liquid droplet, and evaporatedvapor meet. This is due to the proximity to the heated surface. Thecloser to the solid, the higher the mass transfer. Accordingly, certainembodiments include the realization that it can be desirable to have alarger number of narrower channels. For example, higher evaporationrates can be achieved on a surface having ten 100 μm channels than on asurface having five 200 μm channels.

In should be noted that the above-described configuration ofmicrostructures can be advantageous because it may be used to conveyliquids without the use of a pump or pumps. Furthermore, certainembodiments include the realization that microstructured surfaces wouldnot require pumps to direct liquids, as the liquid movement is driven bycapillary action.

Methods of Manufacturing Tubes

As noted above, a tube may be made from one or more extruded polymercomponents. The properties of the extrudate (including composition,surface-modifying agents, methods for increasing surface energy) aredescribed above.

A first manufacturing method is described with reference to FIG. 14. Themethod comprises extruding an elongate conduit having a longitudinalaxis, a lumen extending along the longitudinal axis, and a wallsurrounding the lumen. Microstructures can be pressed or otherwiseformed on the conduit during extrusion. Microstructures can also bemolded, printed, cut, thermoformed, or otherwise formed on the conduitafter extrusion. As shown in FIGS. 4, 8D, and 9D, it was observed thatcutting microchannels into a surface using a sharp object could resultin raised edges around the top portion of the microchannel. Accordingly,in some methods, it can be desirable to grind or polish the surfaceafter microchannel formation to improve surface uniformity. The methodcan also involve corrugating the elongate conduit, such as with acorrugating die. More specifically, the process involves mixing orproviding of a master batch of extrudate material (i.e., material forextrusion), feeding the master batch to an extrusion die head, extrudingthe extrudate as described above, and (optionally) feeding the elongateconduit into a corrugator using an endless chain of mold blocks to forma corrugated tube.

FIG. 14 generally illustrates a setup where there is provided a feedhopper 1401 for receiving raw ingredients or material (e.g. master batchand other materials) to be passed through a screw feeder 1403 driven bya motor 1405 in direction A toward a die head 1407. The molten tube 1409is extruded out of the die head 1411. Conductive filaments canoptionally be co-extruded on or in the molten tube 1409.

An extruder such as a Welex extruder equipped with a 30-40 mm diameterscrew and, typically, a 12-16 mm annular die head with gap of 0.5-1.0 mmhas been found to be suitable for producing low cost tubes quickly.Similar extrusion machines are provided by American Kuhne (Germany),AXON AB Plastics Machinery (Sweden), AMUT (Italy), and Battenfeld(Germany and China). A corrugator such as those manufactured andsupplied by Unicor® (Hassfurt, Germany) has been found to be suitablefor the corrugation step. Similar machines are provided by OLMAS (CarateBrianza, Italy), Qingdao HUASU Machinery Fabricate Co., Ltd (QingdaoJiaozhou City, P.R. China), or Top Industry (Chengdu) Co., Ltd.(Chengdu, P.R. of China).

During manufacture, the molten tube 1409 is passed between a series ofrotating molds/blocks on the corrugator after exiting the extruder diehead 1411 and is formed into a corrugated tube. The molten tube isformed by vacuum applied to the outside of the tube via slots andchannels through the blocks and/or pressure applied internally to thetube via an air channel through the center of the extruder die core pin.If internal pressure is applied, a specially shaped long internal rodextending from the die core pin and fitting closely with the inside ofthe corrugations may be required to prevent air pressure escapingendways along the tube.

The tube may also include a plain cuff region for connection to an endconnector fitting. Thus, during manufacture, a molded-plastic endconnector fitting can be permanently fixed and/or air tight by frictionfit, adhesive bonding, over molding, or by thermal or ultrasonicwelding.

Another suitable method for manufacturing a tube according to theembodiments described here involves spiral forming, as shown in FIG. 15.In general, the method comprises extruding a tape and spirally windingthe extruded tape around a mandrel, thereby forming an elongate conduithaving a longitudinal axis, a lumen extending along the longitudinalaxis, and a wall surrounding the lumen. The method can also includeoptionally corrugating the elongate conduit. Microstructures can bepressed or otherwise formed on the tape during extrusion.Microstructures can also be molded, printed, cut, thermoformed orotherwise formed on the tape after extrusion. In addition,microstructures can also be molded, printed, cut, thermoformed orotherwise formed on the assembled conduit. In some methods, it can bedesirable to grind or polish a surface after microchannel formation toimprove surface uniformity.

The extrusion process involves mixing or providing of a master batch ofextrudate material (i.e. material for extrusion), feeding the masterbatch to an extrusion die head, extruding the extrudate into a tape.

Then, the extruded or pre-formed tape is wound helically. In someembodiments, a reinforcing bead overlays turns of tape. The bead mayprovide a helical reinforcement against crushing for the tube and mayalso provide a source of heat, chemical or mechanical adhesive forfusing or joining the lapped portions of tape.

Shown in FIG. 15 is a molten extruded tube 1501 exiting the die 1503 ofan extruder before passing into a corrugator 1505. On exiting thecorrugator 1505, a heater wire 1507 is wound about the exterior of theformed tubular component.

One advantage of the preferred type of the tube manufacture describedabove with reference to FIG. 15 is that some of the mold blocks B caninclude end cuff features that are formed at the same time as thetubular component. Manufacture speeds can be significantly increased bythe reduction in complexity and elimination of secondary manufacturingprocesses. While this method is an improvement over separate cuffforming processes, a disadvantage of the prior art plain cuff is thatthe corrugator must slow down to allow the wall thickness of the tube inthis area to increase (the extruder continues at the same speed). Thecuff thickness is increased to achieve added hoop strength and sealingproperties with the cuff adaptor fitting. Further, the heat of themolten polymer in this thicker region is difficult to remove during thelimited contact time with the corrugator blocks and this can become animportant limiting factor on the maximum running speed of the tubeproduction line.

Humidification Chamber with Microstructures

Reference is next made to FIG. 7, which shows a humidification chamber129 according to at least one embodiment. The humidification chamber 129generally comprises an inlet 701 and an outlet 703. The chamber 129 isconfigured to be installed on heater plate (discussed above as element131 of FIG. 1), such that base 705 of the chamber contacts the heaterplate 131. The base 705 preferably comprises a metal with good thermalconductivity, such as aluminum and copper. The humidification chamber129 is further configured to hold a volume of a liquid, such as water.In use, the liquid contacts a substantial portion of the base 705. Theheater plate 131 heats the base 705 of the chamber 129, thereby causingat least some of liquid in the chamber 129 to evaporate. In use, gasesflow into the chamber 129 via the inlet 701. The gases are humidifiedwithin the chamber 129 and flow out of the chamber 129 through theoutlet 703.

FIG. 8A shows an example configuration for the microstructures 801 ofthe humidification chamber 129. The properties of the microstructures801 discussed in the preceding section are incorporated by reference. Asshown in this example, the microstructures 801 are arranged verticallyaround a circumference of the humidification chamber 129. In otherwords, the microstructures are perpendicular (or generallyperpendicular) to the base 705 of the chamber 129. The microstructuresin FIG. 8A are shown larger than actual size for illustrative purposesonly. The vertical microstructures 801 carry water 130 up the sides ofthe chamber 129 so that a greater surface area of the water 130 isexposed to the air flow within the chamber 129. In at least oneembodiment, the microstructures extend from the base of the chamber to adistance of 100%, 99%, 95%, between 95-99%, 90%, or between 90-95% (orthereabout) of the height of the chamber 129. The chamber 129 height canbe 50 mm (or about 50 mm). In certain configurations, one or moreadditives, such as SILWET surfactant (Momentive Performance Materials,Inc. of Albany, N.Y. USA) can be included in the water 130 to enhanceuptake by the microstructures.

Although in FIG. 8A, the microstructures 801 are arranged around theentire circumference of the chamber 129, it should be understood that,in certain embodiments, the microstructures 801 are arranged in lessthan the entire circumference. For example, the microstructures 801 canbe arranged in a single portion of the chamber 129 or in random or fixedintervals around the chamber 129.

FIG. 8B shows a first magnified view of a portion of the microstructuresof FIG. 8A. As shown in FIG. 8B, water travels up the verticalmicrostructures 801. Microscale water droplets in or on themicrostructures 801 are exposed to the air flow within the chamber 129.FIG. 8C shows a second magnified view of a portion of themicrostructures of FIG. 8A. As shown in FIG. 8C, air flows through thechamber 129 and across the microstructures 801, causing at least some ofthe water droplets in the microstructures 801 to evaporate. Theevaporated water from the microstructures 801 enters the air flow as avapor.

As shown in the foregoing figures, the microstructures 801 expose agreater surface area of the water 130 in the chamber 129 to the passingair flow, thereby increasing the efficiency of the chamber 129, comparedwith a chamber without any microstructures.

FIG. 8D illustrates a cross section of an example microstructure 801. Inthis example embodiment, the microstructure 801 is a wedge-shapedmicrochannel. The properties of the microstructures described above withrespect to the tube configuration can also be incorporated into themicrostructures for the humidification chamber configuration.

FIG. 9A shows another example configuration for the microstructures ofthe humidification chamber 129. As shown, the microstructures can bearranged vertically and horizontally within the humidification chamber129. The vertically-arranged microstructures are perpendicular (orgenerally perpendicular) to the base 605 and are designated 901, and thehorizontally-arranged microstructures are parallel (or generallyparallel) to the base 705 and are designated 903. Again, themicrostructures are shown larger than actual size for illustrativepurposes only. In general, in the configuration of FIG. 9A, thevertically-arranged microstructures 901 carry water 130 up the sides ofthe chamber 129. The horizontally-arranged microstructures 903 spreadthe microscale water droplets from the vertically-arrangedmicrostructures 901 around the top of the chamber 129, exposing agreater surface area of water to the air flow compared to a chamberwithout any microstructures. The microstructures 901 and 903 therebyincrease the efficiency of the chamber.

FIG. 9B shows a first magnified view of a portion of the microstructuresof FIG. 9A. As shown in FIG. 9B, water travels up thevertically-arranged microstructures 901. When a microscale water dropletreaches the top of its respective vertically-arranged microstructure901, the water droplet then travels along its correspondinghorizontally-arranged microstructure 903 (or group of microstructures).FIG. 9C shows a second magnified view of a portion of themicrostructures of FIG. 9A. As shown in FIG. 9C, air flows through thechamber 129 and across the microstructures 901 and 903, causing at leastsome of the water droplets in the microstructures 901 and 903 toevaporate. The evaporated water from the microstructures 901 and 903enters the air flow as a vapor. In an alternative configuration (notshow), the chamber 129 can be configured to let the water run down themicrostructures with gravity, rather than against it. Moreover, acombination of channels and pins can direct the flow in any desiredfashion.

The vertical microstructures 901 can be similar to those shown above inFIG. 8D and elsewhere in this disclosure and the above discussion oftheir shapes and properties is incorporated by reference here. FIG. 9Dillustrates a cross section of an example horizontal microstructure 903.

The shape and configuration of vertically-arranged microstructures 901and the horizontally-arranged microstructures 903 in FIGS. 9A-9D is forillustrative purposes only. The invention is not limited to thedisclosed embodiment.

For the reasons explained above with respect to the tube embodiments, itcan be desirable to utilize microstructures in combination with asurface having a desirable surface energy, in order to improve thesurface's wettability and water spreading characteristics. Metals andglass are known to have relatively high surface energies and goodwettability. Accordingly, the inner surface of the chamber 129 cancomprise a metal or glass. A metal such as aluminum or copper can bedesirable because these materials also readily conduct heat, which canimprove evaporation rates within the chamber. Glass can be desirablebecause its optical transparency can allow a user to visually inspectthe liquid level within the chamber. Plastics are particularly desirablematerials for the chamber 129 because of their low cost and ease of usein manufacture. As explained above, however, plastics have relativelylow surface energies. Accordingly, it can be desirable to treat theplastic with an additive for increasing surface energy, as explainedabove. In at least one configuration, the chamber 129 wall comprisespoly(methyl methacrylate) plastic with the inner wall coated with alayer of conductive metal, such as gold. In another configuration, theinner surface of the chamber 129 wall comprises a ceramic material,garnet, or a sintered material such as TiO₂.

As noted above, it was discovered that the addition of heat added to amicrostructured surface can dramatically improve evaporation rates.Accordingly, the chamber 129 can incorporate a heating filament in thewall, which can improve heating of the wall and, thus, the likelihoodthat liquid in or on the microstructures will evaporate. In at least oneconfiguration, a heating shroud can be placed around the chamber 129 toimprove heat transfer to the chamber 129. In addition, an insulatingjacket can be placed around the chamber 129 to prevent heat loss andimprove heat retention within the chamber 129.

FIG. 23 illustrates an embodiment of a humidification chamber 2301 thatincludes a number of stacks 2303 having microstructures 2305 on at leastsome of the surfaces of the stacks 2303. As illustrated, the stacks 2303may be arranged as a number of fins or walls; however, otherconfigurations can include towers, columns, or a combination of fins,towers, and columns. As shown, the stacks 2303 can be arranged as finsoriented in the direction of the air flow through the humidificationchamber 2301. However, other configurations could also be used so as toextend into the flow through the chamber 2301 and induce greater mixingand interaction with the microstructures 2305 and, therefore,evaporation. Moreover, in some embodiments, different stacks may havedifferent heights so as to create irregular flow patterns or turbulentflow for the gas passing through the humidification chamber 2301.

In the illustrated embodiment, the humidification chamber 2301 may beheated. In some embodiments, one or more of the plurality of stacks 2303may comprise a thermo-conductive material, such as a metal, to furtherenhance evaporation. In some embodiments all exposed surfaces of eachstack 2303 may incorporate microstructures 2305, which can draw water2307 up from the bottom of the chamber 2301 to portions of the chamber2301 having increased air flow or where the air is less humid and could,therefore, evaporate more of the water. The chamber 2301 is illustratedas a square box; however, other shapes could be used, such asrectangles, cylinders, spheres, domes, etc.

Microstructures can be incorporated into any number of structures withina humidification system. One such structure is the base or bottom of thehumidification chamber itself. In some embodiments, the use ofmicrostructures or irregular surface features on the bottom of ahumidification chamber can disperse a fluid and create a larger surfacearea for enhanced evaporation. In some embodiments, the use ofmicrostructures may act to decrease the depth of the liquid therebyenhancing evaporation. In some embodiments, the microstructures can beconfigured into a pattern, such a lined or straight pattern or acircular pattern. In some embodiments, a lined or straight patternincreases the surface area better than a circular pattern. In someembodiments, there is no pattern and the surface comprises irregularprotrusions or surface irregularities.

Patient Interface with Microstructures

Condensate management is an important issue in the design of patientinterfaces design. Accordingly, certain embodiments include therealization that microstructures can be incorporated into patientinterfaces, including, without limitation, masks (such as tracheal mask,face masks and nasal masks), cannulas, and nasal pillows.

FIG. 10A shows a front perspective view of an example interface 115. Theinterface 115 can be used in the field of respiratory therapy. Theinterface 115 has particular utility with forms of positive pressurerespiratory therapy. For example, the interface 115 can be used foradministering continuous positive airway pressure (“CPAP”) treatments.In addition, the interface 115 can be used with variable positive airwaypressure (“VPAP”) treatments and bi-level positive airway pressure(“BiPAP”) treatments. The interface 115 can be used with any suitableCPAP system.

The interface 115 can comprise any suitable mask configuration. Forexample, certain features, aspects and advantages of the presentinvention can find utility with nasal masks, full face masks, oronasalmasks or any other positive pressure mask. The illustrated interface isa full face mask 1001. The mask 1001 generally comprises a mask assembly1003 and a connection port assembly 1005. The mask assembly 1003generally comprises a mask seal 1007 that, in use, contacts a user'sface.

FIG. 10B illustrates a configuration of the mask 1001 of FIG. 10Aincorporating one or more conductive filaments 1009. As shown in FIG.10B, the conductive filaments 1009 can be arranged in a generallysinuous pattern. However, a variety of configurations are possible, suchas a grid-shaped configuration, a coil, or a ring.

The one or more conductive filaments 1009 can be attached to an outersurface of the mask 1001 wall (that is, the surface of the mask 1001configured to face the ambient air during use). The one or moreconductive filaments 1009 can also be attached to an inner surface ofthe mask 1001 wall (that is, the surface of the mask 1001 configured toface the patient during use). The one or more conductive filaments 1009can also be embedded or otherwise incorporated in the mask 1001 wall.The last configuration can be desirable because it can prevent a patientfrom touching the conductive filaments 1009. A combination of theforegoing configurations can also be incorporated in the mask 1001.Moreover, the mask 1001 wall itself, or at least a portion of the mask1001 wall, can be conductive. For example, the mask 1001 can comprise aconductive polymer or a conductive metal.

FIG. 11A is a rear elevation view of the mask 1001 of FIG. 10. FIG. 11Agenerally illustrates an example configuration for microstructures 1101on the inside surface of the mask. The properties of the microstructures1101 discussed in the preceding sections are incorporated by reference.The example mask 1001 has a longitudinal axis LA and a transverse axisTA. The mask 1001 comprises a first portion 1103 on one side of thelongitudinal axis LA and a second portion 1105 on the other side of thelongitude axis LA. In general, the microstructures 1101 extend along theunderside of the mask 1001 parallel the transverse axis TA. Themicrostructures 1101 on either side of the longitudinal axis LA formmirror image patterns. The microstructures 1101 are not drawn to scaleand are for illustrative purposes only.

FIG. 11B shows a first magnified view of a portion of themicrostructures 1101 of FIG. 11A. FIG. 11C illustrates a cross sectionof an example microstructure 1101. In this example embodiment, themicrostructure is a microchannel. The microstructures can be similar tothose discussed above, and the discussion of their shapes and propertiesis incorporated by reference here.

As explained below, certain embodiments include the realization thatincorporating microstructures in a patient interface can improvecondensate management by preventing or reducing formation of macroscalewater droplets (that is, water droplets having a diameter greater than1000 μm (or about 1000 μm). FIG. 12A shows a schematic of water dropletformation on an interface surface that does not incorporatemicrostructures. In contrast, FIG. 12B shows a schematic of waterspreading on an interface surface that does incorporate microstructures.In both figures, 1201 designates the outer surface of the interface(that is, the surface of the interface configured to face the ambientair during use), and 1203 designates the inner surface of the interface(that is, the surface of the interface configured to face the patientduring use).

Patient interfaces experience very high humidity conditions. As shown inboxes 1205 and 1207, water droplets can readily form on the innersurface of a patient interface when the inner surface 1203 of theinterface is smooth (or relatively smooth). As shown in box 1209, inuse, these water droplets will run down to a lower area of the patientinterface and pool together or drip onto a patient's face. As shown inboxes 1211 through 1213, the incorporation of microstructures on theinner surface 1203 of a patient interface can ameliorate this problem.As shown in boxes 1211 and 1213, the microstructures spread out thecondensate along the length (or at least a portion of the length) of themicrostructures, which prevents the condensate from forming droplets. Asshown in box 1215, because condensate spreads out along themicrostructures over a large surface area, the condensate can evaporatemore readily. This spreading action also decreases the likelihood thatcondensate will pool in a lower area or drop on the patient's face. Incertain embodiments, incorporation of microstructures on the innersurface 1203 allows condensate to be redirected from the patientinterface onto an absorbent layer (not shown), such as a sponge orbreathable membrane.

FIG. 11D shows a rear elevation view of the mask 1001 of FIG. 10A. FIG.11D schematically illustrates condensate spreading out along themicrostructures 1101 on the inner surface of the mask.

In at least some configurations, the one or more conductive filaments1009 (FIG. 10B) comprise one or more heating filaments configured toheat the mask 1001 wall. When the one or more conductive filaments 1009comprise at least one heating filament, the heating filament can beconnected to an electrical supply and thereby apply heat to the mask1001 body. As shown in FIG. 13, the added heat speeds evaporation ofcondensate spread out in or on the microstructures.

The foregoing description of the invention includes preferred formsthereof. Modifications may be made thereto without departing from thescope of the invention. To those skilled in the art to which theinvention relates, many changes in construction and widely differingembodiments and applications of the invention will suggest themselveswithout departing from the scope of the invention as defined in theappended claims. The disclosures and the descriptions herein are purelyillustrative and are not intended to be in any sense limiting.

What is claimed is:
 1. A component for use in a medical circuitcomprising: a reservoir portion configured to hold a liquid; anevaporator portion adjacent the reservoir portion configured tofacilitate evaporation of the liquid; a microstructured surface disposedabout a side of the reservoir portion, the microstructured surfaceconfigured to transport liquid up the side from the reservoir portionaway from a base of the reservoir portion to the evaporator portion. 2.The component of claim 1, wherein the evaporator portion is heatable. 3.The component of claim 1, further comprising at least one raisedstructure upon which the microstructured surface is located.
 4. Thecomponent of claim 3, wherein the raised structure comprises one or moretowers.
 5. The component of claim 4, wherein the towers have a lengththat is greater than both a height and a width.
 6. The component ofclaim 1, wherein the microstructures are configured to be aligned with aflow path of a gas flowing through the evaporator portion of thecomponent.
 7. The component of claim 1, wherein the component is achamber suitable for use with a humidifier unit.
 8. The component ofclaim 7, wherein the chamber comprises walls configured to be heated bya heater base of the humidifier unit.
 9. The component of claim 7,wherein the chamber comprises walls configured to be heated by a heatingmember distinct from the humidifier unit.
 10. The component of claim 7,further comprising insulation disposed at least on or over a wall of thechamber near the evaporator portion.
 11. The component of claim 7,wherein microstructured surface comprises vertical microstructuresconfigured to carry liquid up the sides of the chamber so that a greatersurface area of the liquid is exposed to the air flow within thechamber.
 12. The component of claim 1, wherein the component forms atleast a portion of an inner wall of a chamber suitable for use with ahumidifier unit.
 13. The component of claim 1, wherein themicrostructured surface is integral to the side.
 14. The component ofclaim 1, wherein the microstructured surface comprises microchannelsextending generally horizontally near the reservoir portion.
 15. Thecomponent of claim 1, wherein the microstructured surface comprisesmicrochannels extending generally vertically near the evaporatorportion.
 16. The component of claim 1, wherein the microstructuredsurface comprises microchannels extending generally horizontally nearthe evaporator portion.
 17. The component of claim 1, wherein themicrostructured surface comprises microchannels extending generallyvertically near the evaporator portion and microchannels extendinggenerally horizontally near the evaporator portion, wherein the secondmicrochannels are configured to transport liquid to the thirdmicrochannels.
 18. The component of claim 1, wherein the microstructuredsurface comprises a substrate having an equilibrium contact angle lessthan π/2 radians.
 19. A component for use in a medical circuitcomprising: a reservoir portion configured to hold a liquid; anevaporator portion adjacent the reservoir portion configured tofacilitate evaporation of the liquid; a microstructured surfaceconfigured to transport liquid from the reservoir portion to theevaporator portion, wherein the microstructured surface comprisesmicrochannels having an aspect ratio that is lower near the reservoirportion and higher near the evaporator portion, the aspect ratioincreases along a gradient.
 20. A component for use in a medical circuitcomprising: a reservoir portion configured to hold a liquid; anevaporator portion adjacent the reservoir portion configured tofacilitate evaporation of the liquid; a microstructured surfaceconfigured to transport liquid from the reservoir portion to theevaporator portion, wherein the microstructured surface comprises firstmicrochannels extending generally horizontally near the reservoirportion and second microchannels extending generally vertically near theevaporator portion, wherein the first microchannels are configured totransport liquid to the second microchannels.